The present invention concerns a procedure for regulating the evaporation rate and the layer buildup in the production of optically effective thin layers in a vacuum on substrates with controlled evaporator power and with continuous measurement of the optical behavior of the deposited layer.
In the description of this invention, "optical behavior" means the influence on the amplitude, phase and the spectral dependence of the light (used for measurement) by the layer under consideration. Deposited, optically effective layers change, for example, transmission, reflection, phase and state of polarization of the measuring light. These effects can be used for measuring purposes as described below.
It is known in the art how to influence the evaporation rate of substance required in the production of thin layers by controlling the energy supply. It is also known in the art how to determine the transmission of reflection behavior of the deposited layer by means of a light or a light bundle, for German Pat. DT-AS No. 1 548 262. The result of such measurement is usually used to interrupt the evaporation process after attaining certain layer properties. The evaporation time determining the properties of the deposited layer is not influenced thereby. Finally it is also known to follow layer buildup as a function of time and to interrupt the evaporation process by continuously monitoring the transmission or reflection behavior of monochromatic light and counting the maximums or minimums. The number of maximums or minimums, dependent on the wavelength of the light used, permits an inference as to the thickness of the layer (German Pat. DT-AS No. 1 214 970). Also with this known measuring method, only the layer thickness, but not the duration of their production is involved.
In this application, the term "optically effective layers" will include all layers which change the optical properties of the substrate. They may be reflection-reducing layers, filter layers on lenses and other glasses which reflect or transmit, part of the electromagnetic radiation in the visible and/or invisible range. The wavelength range under consideration in this application extends from ultraviolet to the far infrared. The optical effectiveness relates, above all, to low-loss amplitude changes of the reflected or transmitted radiation. It also includes layers which change the phase or the polarization state of the light used for the measurement.
Optically effective layers may have both a homogeneous or (in an individual layer) nonhomogeneous composition or may consist of a combination of a number of layers with low and high refractivity, as are encountered, for example, with the so-called interference filters which have the remarkable property of compensating to a great extent errors in the thickness of individual layers, if the individual layers have the optical thickness of quarter-wavelengths of the light used for measurement of multiples thereof. This presupposes, however, that the subsequent layer grows together with the preceding layers till the desired properties are reached. Hence, not the properties of the individual layer, but the effect of the totality of the layers determine the effect attained. From this follows, that especially multiple layers of the stated type may be manufactured only by using optical measuring procedures, but not by using mechanical measuring procedures, in order to obtain the desired close tolerances. For example, weighing methods cannot determine the partial or total optical effect. When using a quartz resonator for determining layer thickness, the type and the partial pressure of the unavoidable gas remainder in the vacuum chamber play an appreciable part in view of the accuracy of the measurement result.
In view of the overall properties of optically effective thin layers, recently progressively closer tolerances have been determined. This presupposes that the manufacturing method for the layers is, to a high degree, reproducible in order to obtain always layers with the same constant characteristics. This does not only apply to the numerous surface layers of complex optical systems, but especially for eyeglasses, in particular sunglasses. It is self-understood that, for example, in case of eyeglass breakage, replacement by a glass with different optical properties is not permissible. Color differences are particularly intolerable.
Accordingly, it is an object of the present invention to provide a procedure for obtaining high reproducibility of all properties of optically effective layers during their manufacture with extremely simple operation of the evaporator device.
Another object of the present invention is to provide an arrangement of the foregoing character which may be economically fabricated and has a substantially long operating life.
A further object of the present invention is to provide an arrangement, as described, in which the component parts are readily accessible for maintaining them in service.